In conventional internal combustion engines for vehicles, particularly, the valve train includes hydraulic lash adjuster means to take up the lash or operating clearance in the valve train. The hydraulic valve adjuster includes an oil filled pressure chamber which receives oil from a reservoir chamber to provide an automatically axially adjustable member taking up the aforesaid clearance space. In conventional engines, the reservoir chamber is continuously supplied with oil from a pressurized oil line which is the same oil line which lubricates the bearings of the camshaft or other valve train components. Obviously, it is costly to provide an oil passage in the cylinder head of the engine for the valve adjusters. The following list of U.S. patents disclose this conventional externally supplied lash adjuster system: U.S. Pat. Nos. 1,792,836; 2,815,012; 3,153,404; 3,352,293; 3,502,058; 4,462,364; 4,463,414; and 4,481,913.
There have been previous attempts to eliminate the external oil supply line to lash adjusters. The U.S. Pats. Nos. 4,191,142 and 4,457,270 disclose hydraulic lash adjusters with essentially sealed reservoir chambers and means in the form of a flexible diaphragm to permit volumetric changes of the oil in the reservoir to take place. Essentially, these lash adjusters are separate oil machines without any connection to the engine oiling system. However, the devices are of complicated design and they present problems over time due to leakage of oil from the reservoir despite the use of seals to prevent such leakage.
Another attempt to eliminate pressurized oil passage supply means for a lash adjuster is disclosed in U.S. Pat. No. 3,875,908. In this patent, a lash adjuster is disclosed without external pressurized oil passage means for the lash adjuster, but instead, the lash adjuster receives oil which drips from a member 3 into a central opening in the upper part of the lash adjuster. The opening or oil inlet extends axially through the upper portion or plunger of the lash adjuster and is communicated with the reservoir of the lash adjuster. Thus, the supply to the lash adjuster's reservoir depends solely on the collection of oil and the downward movement thereof by gravity to supply the reservoir. Also, the reservoir is essentially open to the interior space of the engine and, thus, not protected from contamination therein.
The subject hydraulic lash adjuster, like the device discussed in the previous paragraph, does not require the provision of an external pressurized oil line to maintain oil levels in the lash adjuster reservoir chamber. However, the subject lash adjuster utilizes a positive pumping action produced by operation of the engine to cause oil collected near the upper surface of the lash adjuster to be directed into the reservoir chamber. It has been discovered that a desirably fitted reservoir plunger within a sufficiently diametered chamber of the lash adjuster housing will be moved in a cocking or oscillating manner by the associated rocker arm which is periodically moved by the lobe of a camshaft in an overhead cam type of engine. This oscillating or cocking action of the reservoir plunger can only be achieved when the fitting between the reservoir plunger and the cylinder bore is adequate to permit this movement. This is in contrast to the very tight precision fitting of the lower power plunger of the lash adjuster which typically is in the order of a clearance of 0.00005 inches. It has been found that if the clearance between the upper reservoir plunger and the cylinder bore is about 0.002 inches, the aforementioned oscillation or side-by-side cocking of the plunger is sufficient to positively cause oil collected around the upper surface of the plunger and the housing to be pumped into the reservoir chamber in a positive manner.
Therefore, it is the object of this invention not only to eliminate the need for an external pressurized oil supply line for lash adjusters, but also to utilize the collected oil falling on top of the lash adjuster for replenishing the reservoir by means of a positive pumping action produced by the valve train of an internal combustion engine.
Further advantageous features and objects of the invention will be more readily apparent from a reading of the following Detailed Description of an Embodiment, reference being had to the accompanying drawings in which the preferred embodiment is illustrated.